Apparatus for gravity separation of granular material



A. A. HIRST 2,320,519

APPARATUS FOR GRAVITY SEPARATION OF GRANULAH MATERIAL June 1 1943,

Filed Jan. 7, 1941 3 Sheets-Sheet l INVENTOR ARTHUR A, HIRST QJgLMAMM;

June 1, 1943. HlRgT 2,320,519

APPARATUS FOR GRAVITY SEPARATION OF GRANULAR MATERIAL Filed Jan. '7,1941 3 Sheets-Sheet 2 ATTORNEYS June 1, 1943. s-r 2,320,519

APPARATUS FOR GRAVITY SEPARATION OF GRANULAR MATERIAL Filed Jan. '7,1941 3 Sheets-Sheet 3 1- Z\O4- F L I fiT--/ I 5e 5e 3;} I01 6 86 as a 30 Q5 84 as a o $68 as so INVENTOR B7 ARTHUR AHmsT ATTORNE vs PatentedJune 1, 1943 APPARATUS FOR GRAVITY SEPARATION OF GRANULAR MATERIALArthur Algernon Hirst, Northfield, Birmingham,

England, assignor of one-half to Simon- Carves Limited, Cheadle Heath,Stockport,

England Application January 7, 1941, Serial No. 373,512 In Great BritainDecember 30, 1939 12 Claims. ((31. 209--173) This invention relates tomethods and apparatus for gravity separation of granular material suchas coal or ores and of the type in which the granular particles separateaccording to density in a separating fluid consisting of a suspension offinely comminuted solid in .water or other liquid.

Known apparatus of this type has included a separator with or without areserve or surge tank, the separated products being caused to pass overa screen or screens, of perforated metal, wire cloth or the like, thesuspension draining off the separated products without spraying of thelatter, being returned either to the separator or to the reserve tankwhilst dilute suspension resulting from the spraying of the separatedproducts either with fresh water or with process water, i. e. thatobtained from settling tanks and the like, was passed to a dilutesuspension tank from which latter the dilute suspension was pumped to asettling cone or other type of thickener provided with outlets forthickened suspension and for liquid wholly or partially clarified.

The primary object of this invention is'to provide an improved methodenabling the density of the separating suspension in the separatorautomatically to be maintained substantially constant.

A further object is to provide an improved and simplified apparatus forcarrying the improved method into effect.

Referring to the drawings:

Figure 1 shows diagrammatically one arrangement according to thisinvention.

Figure 2 shows, to an enlarged scale, a part of same.

Figure 3 is a sectional plan view on line 33 of Figure 2.

Figure 4 is a perspective view of a modification.

Figure 5 shows diagrammatically a further arrangement.

One form of apparatus according to this invention illustrated in Figures1 to 3 includes a separator in the form of a relatively shallow vesselor trough 6 provided at each end with a sloping base 1 so that at suchends the depth increases gradually from the end of the separator towardsthe central portion where the base 8 is either flat or curved. v

The separator may be ofthe form described in either of our applicationsNos. 338,131 or 338,132, and is divided by a transverse partition 9 intoan inlet compartment on the right i which the material passes into theinlet compartment.

Circulating through the separator isa separating fluid comprising asuspension of finely comminuted solid in water, such comminuted solidbeing hereinafter referred to for the purpose of convenience as sand.

The clean coal, ,or lighter particles, floating in the suspension in theinlet compartment are removed over a clean coal outlet H by a combconveyor I0 and pass down a chute IS on to a screen l9, whilst the heavydirt, sinking in the suspension, is carried beneath the partition 9 bythe scraper l2 and is removed by the latter over a dirt outlet 20 andfalls on to a screen 2 I.

The suspension is circulated through the separator and a reserve orsurge tank 5, and any suspension removed with the clean coal and dirt isdrained from these separated products on the first portion of each ofthe screens l9 and 2|, is collected in vessels 22 and is returned fromthe latter to the reserve tank by pipes 23.

When merely drained to remove excess suspension, the separated productshave accumulations of sand adhering to the separated partioles and suchproducts are accordin ly subjected to a spraying operation on thescreens l9 and 21 to wash away the sand accumulations leaving theseparated products relatively clean.

The separated products may be sprayed either with fresh water or asillustrated with process water, i. e. the clarified liquid obtained fromsettling tanks or the like and pumped to the sprays through pipes 24from a tank 25. Alternatively, the separated products may be sprayedpartly with process water and partly with fresh water: for example, thefinal clean coal sprays may be supplied with fresh water and theremaining sprays with process water. The dilute suspension resultingfrom this spraying opera- Hon is collected in vessels 25 and passed bypipes 21 to a dilute suspension tank 28 in the form of a relativelysmall collecting cone or trough.

The dilute suspension passes through a fine mesh slurry screen at thetop of the dilute suspension tank 28, this screen Operating to removecoarse particles or foreign material separating with the products andremoved therefrom during the spraying operation.

Dilute suspension from this tank 28 is pumped through a. pipe 29 intothe top of a settling cone or thickener 30 having an overflow rim 3! forclarified suspension.

The settling cone functions as a thickener by permitting thickenedsuspension to accumulate in the lower portion whilst clarified liquidcollects in the upper portion and overflows the rim 3| An overflow pipe4 leads from the rim 3| to .the spray tank 25 but for convenience ofillustration this pipe is shown partly broken away.

The thickened suspension passes from the base of the settling cone downa pipe 32 in which is an on-ofi' valve 33A and an interchangeable jet ornozzle 33 and this suspension is delivered into a thickened suspensioninlet 34 extending through the top of a conditioning or mixing vessel 35suspended from one end of a balance arm 36 pivotally supported at 31 andprovided at its other end with an adjustable balance weight 38.

The jet or nozzle can be screwed on and off or otherwise readilydetachable to enable easy and rapid changing of the size of the jet ornozzle.

Regulation of the discharge of thickened suspension from the cone orthickener is efiected by interchanging jets of different internal sizesor bores.

A smaller jet or nozzle results in thicker suspension discharged fromthe cone or thickener and vice versa.

Clarified liquid from the rim 3i passes down a pipe branched into twopipes 39 and 58 in each of which is a. valve 40. At the lower end of thepipe 39 there is a flexible portion 4| to the lower end of which isconnected a cable 42, one end of which is anchored to the balance arm 36whilst the other end carries a weight 43.

As will hereinafter be described the flexible pipe 42 is displaceable toenable delivery of clarifled liquid to one or other of two receptacles44 and 45, the former of which delivers to a clarified liquid inlet 46extending through the top of the vessel-35, whilst from the receptacleextends a pipe 41 discharging into the tank 25.

Details of the conditioning vessel are shown in Figure 2 from which itwill be seen that the vessel has an inverted conical lower portion intothe base of which extends a pipe 48 for the supply of compressed air toform an air lift in the vessel for mixing the material and preventingsettling of the sand in the conditioning vessel.

A circulating pipe 49 extends centrally through the vessel from a pointslightly spaced from the base of the vessel to a point near the top ofthe vessel approximately at the normal liquid level therein.

The nozzle 50 to which is connected the flexible pipe 48 projectsupwardly through the base of the vessel 35 and into the lower end of thecirculating pipe 49 and discharge of compressed air through the nozzle50 forms an air lift up the pipe 49 to circulate the material within thevessel 35.

A baffle 5| is supported above the upper end of the circulating pipe 49.

Slots 52 formed in the wall of the conditioning vessel near the topthereof permit overflow of conditioned suspension from this vessel andsuch overflow is directed by the spout 53 to one or other of a pair ofsuperposed chutes 54 and 55, the former of which delivers through a pipe56 into the top of the reserve tank, whilst the chute delivers through apipe 51 to the dilute suspension tank 28, without going through theslurry screen ll mounted above this tank.

The branch pipe 58 leading from the rim 3i of the settling coneterminates in a flexible portion 59 for delivering clarified liquid toone or other of two receptacles 60 and Bi, discharging respectivelythrough a pipe 62 to the tank 25 and a pipe 53 to the reserve tank 5. v

Within the reserve tank 5 is a float 64 mounted on the lower end of afloat rod 65 connected to one end of a balance arm 66 pivoted at 61 andprovided at its other end with an adjustable balance weight 68.

Mounted on the arm 66 is a switch 69 preferably in the form of a mercuryswitch for controlling the energisation of a solenoid coil 19 from thesupply mains H.

The flexible pipe 59 is coupled to the slidable core 12 of the solenoidand to a spring 13 which in the unenergised position of the solenoidholds the pipe 59 in the position shown in Figure 1 in which itdischarges into the receptacle 60. When the solenoid is energised thecore 12 is moved to displace the pipe 59 from this position and againstthe action of the spring 13 so as to divert the discharge of clarifiedliquid from the pipe 59 into the receptacle 6|.

The reserve tank has an overflow pipe 14 for passing overflow liquidfrom the reserve tank on to the slurry screen II above the dilutesuspen-' sion tank 28 from which tank it is pumped back to the thickener30.

An adjustable stop 15 is provided beneath the weight 43 so that thecable 42 is slack for the normal movement of the balance arm 36,becoming taut only when the medium in the vessel 35 becomes greater thana predetermined maximum as hereinafter referred to.

Suspension is returned to the tank 6 from the base of the reserve tank 5though a pipe 11 in which is a pump I6.

The operation of the apparatus is as follows:

The granular material separated in and removed from the trough 6 isdrained on the screens l9 and 21 and the suspension collected in thevessels 22 is passed to the reserve tank 5 to be pumped back to theseparator through the pipe 11. I

The dilute suspension resulting from the spraying of the separatedproducts is passed to the dilute suspension tank 28 from which it ispumped into the thickener 30 in which the suspension is thickened up togive thickened suspension in the base of the thickener and clarifiedliquid overflowing to the rim 3|.

The size of nozzle 33 is chosen so that thickened suspension'leaving thebase of the thickener through the pipe 32 is denser than the suspensionin the main separator 6 and the density of thickened suspension shouldnormally never become less than that of the suspension in the separator.

Thickened suspension is allowed to flow continuously from the thickener30 into the conditioning vessel 35 as fast as it is formed in thethickener and without regulation of the volume.

In this Way simplification of the system is possible, particularly whenmore than one cone or thickener is employed, whilst the tendency for thebottom outlet of the cone or thickener to become choked is considerablyreduced.

The material in the conditioning vessel is maintained homogeneous by theaction of the air lift which is to draw material from the base of thevessel into the lower part of the circulating pipe and force thismaterial up the pipe to discharge it into the top of the vessel.

In Figure 1 the conditioning vessel is shown in its normal positionwhich, by choice of nozzle 33 and the adjustment of the balance weight38, has been set such that the density of the suspension in theconditioning vessel is at a predetermined figure greater than that ofthe suspension to be passed to the separator. For example, thepredetermined density figure may be approximately 1.5 for an operatingdensity of 1.45 in the separator.

In this position of the conditioning vessel the overflow from the rim 53passes down the chute 54 and pipe 56 into the reserve tank and theclarified liquid passing down the pipe 39 is directed by the diverterpipe 4| into the receptacle 45 and via the pipe 41 to the spray tank 25.

Adjustment of the density of the suspension to be returned into theseparating vessel from the reserve tank is effected by keeping thedensity of conditioned suspension at the predetermined figure greaterthan that of the suspension to be passed to the separator and adjustingadmission of clarified suspension to the reserve tank through the pipes58, 59 and 53 in accordance with the indications of the denslmetriccontrol comprising the float 64 and the mechanism associated therewith.i

In the position shown in Figure 1 the flow of clarified liquid along thepipe 58 is directed by the diverter pipe 59 into the receptacle 60 andpasses down the pipe 52 to the spray tank 25, this being the arrangementwhen the densimetric control indicates a correct or light density in thereserve tank.

If the density of the suspension in the reserve tank rises above thepredetermined figure the float 54 rises and the switch 69 on the balancearm 65 is closed to energise the solenoid coil and the pipe 59 is movedto the right as shown in Figure 1 to divert the fiow of clarified liquidinto the receptacle 6! and thus via the pipe 63 into the reserve tank 5.

Admission of clarified liquid to the reserve tank reduces the density ofthe suspension in the tank and when this density falls to or below thecorrect figure the float 64 falls to permit the balance arm 66 to returnto its normal position as defined by a stop and the flow of clarifiedliquid is diverted back to the spray tank 25.

The power required to operate the balance arm to close the switch 69governs the sensitivity of the control and in order to regulate thissensitivity it is desirable that the balance arm 68 should be providedwith a control for varying the sensitivity.

The conditioning vessel is suspended from the balance arm 36 forsubstantially vertical movement so that so long as the density of thesuspension in the vessel is greater than the predetermined figure, whichis itself equal to or greater than the operating density in theseparator (being say 1.5 for an operating density of 1.45) theconditioning vessel is in the position shown in Figure 1 and theoverflow from the vessel 35 is delivered to the reserve tank as abovedescribed.

If, however, the suspension in the vessel 35 be- 3 comes less dense thanthe above mentioned predetermined figure the vessel 35 rises and theoverflow from the rim 3| is directed to the chute and via the pipe 5"!to the dilute suspension tank 28 whence it is returned through the pipe29 to the thickener 30.

If the suspension in the vessel 35 becomes too dense the vessel fallsfrom the position shown in Figure 1 and this movement tightens the cable42, which as previously described, is slack for the normal movements ofthe balance arm, and whilst the overflow from the spout 53 is stilldelivered down the chute 54 to the reserve tank the diverter pipe 4| ispulled by the cable 42 to the left as seen in Figure 1 and clarifiedliquid from the rim 3i is delivered to the conditioning vessel until thedensity has been reduced in the desired manner.

Thus, the conditioned suspension returned to the reserve tank isprevented from becoming so dense as to cause sluggish fiow in thecirculating pipes, whilst as soon as the density falls below thepredetermined minimum figure the fiow of suspension from the vessel 35to the reserve tank is cut off and this suspension is returned via thetank 28 to the thickener 30 to be thickened up.

When the suspension in the vessel 35 has been sufiiciently diluted thevessel rises to allow the weight 43 to return to its stop 15 andtransfer the flow of clarified liquid to the receptacle 45.

The density of the suspension returned to the reserve tank from thevessel 35 is in this way kept automatically between predetermined limitswhich, for an operating densi y of .45 m t be. for example. 1.5 and 1.7.

This conditioned suspension at a density greater than that of thesuspension for the main separation treatment is mixed with thesuspension in the reserve tank and the density is adjusted in thisreserve tank by adjusting the admission of clarified suspension throughthe pipe 63 in accordance with the indications of the densimetriccontrol.

If desired the suspension may be circulated within the reserve tank bymeans of an air lift such as provided in the conditioning. vessel 35 orby means of a circulating pipe provided with a pump acting to withdrawsuspension from the lower part of the reserve tank and discharge it intothe upper part.

With the arrangement described above the control is simpl fied in thatit is necessary to regulate only the flow of clarified liquid and aslong as there is sufiicient medium in the system and the thickener isworking efi'ectively, the reserve tank can be kept full, thusmaintaining constancy of pumping.

Further, an indication of insufiiciency of medium will be given by thefalling level of suspension in the reserve tank.

It may. however, be desirable or convenient to cut off the fiow ofthickened suspension from the vessel 35 to the reserve tank for theperiods dur- 7 ing which clarified liquid is being admitted to thereserve tank and for this purpose a simple on-off control such as shownin Figure 4 may be utilised.

In this arrangement the pipe 56 conditioned or thickened suspension tothe reserve tank extends to a position adjacent the diverter pipe 59 forclarified liquid and this pipe 56 is provided with a diverter pipe 78similar to the pipe 59.

Thetwo diverter pipes are coupled together by a cable 19 passing round apulley 80 and confor delivering v nected at one end to the solenoid I2and at the other end to the spring I3.

Beneath the end of the diverter pipe 16 there is arranged a pair orreceptacles 6i and 92 similar to the receptacles 60 and SI below thepipe 59 as already described.

A receptacle 6| is connected by a pipe to the dilute medium tank 28whilst the receptacle 82 leads to the reserve tank.

In the position shown in the drawings the solenoid is energised todivert the flow of clarified liquid into the receptacle 6| for passagedown the pipe 63 to the reserve tank and this movement of the solenoidalso diverts the flexible pipe 18 so that the conditioned medium flowingdown-the pipe 56 is diverted into the receptacle BI and thence to thedilute medium tank 20 instead of to the receptacle 92 and thence to thereserve tank.

As soon as the densirnetric control indicates the correct density theswitch 69 is opened to cut of! the supply to the solenoid coil 10 andthe spring I3 returns both the diverter pipes 59 and 19 to their normalpositions in which the pipe 59 directs the clarified liquid va thereceptacle 60 to the spray tank 25 whilst the conditioning suspensionfrom the pipe 56 flows via the receptacle 82 to the reserve tank. 1

In the constructions described above each of the on-off controls,namely, for clarified liquid in Figures 1 to 3 and both for clarifiedliquid and th ckened suspension in Figure 4, is of the continuous flowtype including a movable diverter pipe arranged in the flow of liquid orsuspension and movable between two positions.

With such a control the flow is not dammed up or impeded since in theoff position of the control, although the flow is cut off in relation tothe reserve tank, this flow is merely diverted to a further tank andrecirculated. This is particularly advantageous in the case of thethickened suspension to avoid choking of the system due to accumulationsof suspension during the periods when the flow to the reserve tank iscut off.

Such a control is, however, somewhat inflexible in that in the onposition it permits full flow of liquid or suspension whilst in the offposition such flow is cut oil completely.

The modified control illustrated in Figure 5, however, enables variationin steps from zero to maximum of the flow to the reserve tank bothofclarified liquid and of thickened suspension.

The two pipes 56 and 58, for thickened or conditioned suspension andclarified liquid respectively, are arranged side by side eachterminating n a fish tail distributor with a serrated lower edge.

Mounted beneath these pipes is a shutter 64 having three side-by-sideinverted conical chutes 85, 96 and 81 connected respectively to thespray tank 25, the reserve tank and the dilute suspension tank 28through pipes 68, 69 and 90 each of which includes,a flexible portion.

The shutter 84 is guided in bearings 9| for horizontal sl ding movementbackwards and forwards beneath the ends of the pipes 56 and 56.

One form of operating mechanism for the shutter includes an eccentric 9Ion a power driven shaft 92 arranged to reciprocate endwise in ahorizontal direction a rod 93 with which is associated a member 94carrying a pair of pawls 95 and 96 for engagement one with each of twinratchet racks 9'! and 98 mounted side-by side on the shutter with theteeth of one rack facing in the opposite direction to the teeth oi theother rack.

Compression springs 99 on the rod 93 locate the pawl carrying member 94resiliently in position relative to the rod 93 so that a yieldable driveis provided for the shutter to prevent the latter straining against thelimiting stops I00.

Each pawl is pivoted to the member 94 and is. held in an inoperativeposition clear of its associated rack by a spring IOI, each pawl beingconnected by a link to one of a pair of solenoids I02 and I03 theenergising coils of which are adapted selectively to be connected to apair of supply mains I04 through a two-way mercury switch I05 mounted onthe balance arm 66 of the densirnetric control including float 64 in thereserve tank 5 as described with reference to Figures 1 to 3. The coreof the solenoids I02 and I03 pull downwards when energised so as toengage one or other of the pawls with its corresponding rack.

In the position illustrated, the shutter is in one terminal positionengaging the right hand stop I00 and the flow of thickened suspensionfrom the pipe 56 is diverted from the reserve tankto the dilutesuspension tank 28, whilst the flow of clarified liquid from the pipe 56is directed into the reserve tank via the chute 96 and pipe 69.

When the float 64 falls in response to a fall in density in the reservetank, as a result of the admission of clarified liquid, the balance arm66 tilts the mercury switch to energise the left hand solenoid I02 so asto move the pawl 95 into engagement with the rack 99 whereupon thereciprocation of the pawl carrier by the eccentric 9I causes the shutterto slide to the left as seen in the drawings.

Such movement takes the chute 06 partly under the distributor oi thepipe 56 and partly from under the distributor of the pipe 56. Thus somethickened suspension flows into the reserve tank instead of all flowingto the dilute suspension tank whilst the flow of clarified liquid to thereserve tank is reduced as part of this flow passes down the chute 85 tothe spray medium tank 25.

The proportion of thickened suspension to clarified entering the chute86 depends on the time for which the pawl is held down to engage therack 98, i. e., upon the period for which the solenoid I02 is energised,this period being governed by the densirnetric control.

The rate of reciprocation of the shutter is slow so that after eachadjustment there is suflicient time for the conditions within theapparatus to stabilise itself.

When the density of suspension in the reserve tank reaches thepredetermined minimum the float 64 rises and the solenoid I02 isde-energised to permit the spring IN to return the pawl 95 to itsinoperative position,

The shutter now remains in its adjusted position, although the pawlcarrier and pawls continue to reciprocate under the operation of theeccentric 9I, until the densirnetric control again indicates anincorrect density in the reserve tank.

If the suspension in the tank 5 becomes too dense, the float 64 risesand tilts the mercury switch in the opposite direction to that in theprevious case and the solenoid I03 is operated to move the pawl 96 intoengagement with the rack 91 so that the shutter is moved to the right asseen in the drawing. Such movement results in a reduction of the flow ofthickened suspension and an increase in the flow of clarifled liquid tothe reserve tank so as to decrease the density of the resultantsuspension in the reserve tank.

In a further construction the arrangements shown in Figures 1 and 5 arecombined and the total flow of conditioned suspension from theconditioning vessel is delivered to the reserve tank by the chute 54 andpipe 56 whilst the admission of clarified liquid to the reserve tank isvaried in step according to the indications of the densimetric float(64, I05 or I06).

Such a construction includes a conditioning vessel 35 on balance arm 36,this chamber'receiving thickened suspension from the cone or thickener30 and delivering conditioned suspension to the reserve tank via chute54 and pipe 56 whilst, for the control of the flow of clarified liquid,a shutter such as 84, but omitting the parts 56, 87 and 90, could beused, together with the densimetric float 64, balance arm 66, mercuryher from a further tank filled switch I05, solenoids I02 and I03 andassociated part for operating the shutter 84 as previously describedwith reference to Figure 5.

In operation the total flow of conditioned suspension passes to thereserve tank as described with reference to Figure 1 and the flow ofclarifled liquid only is controlled by the shutter 84 as described withreference to Figure 5.

Instead of providing a mixing or conditioning chamber as describedhereinbefore to guard against the settling tank failing to givesufiiciently thickened suspension a densimetric control can be providedoperating in a chamber or vessel interposed between the orifice in thebase of the settling tank and the chute leading to the mixing device.

This further control, which may be adjusted with bottom control only,that is a mercury switch or the like operating when the float falls, isarranged so that a further pivoted or sliding chute is caused tointerrupt the under flow of thickened suspension passing from thesettling tank into the chute leading to the mixing device, this furtherchute diverting the flow either direct to the top of the settling tankor to the dilute suspension tank. I

Preferably the further chute is arranged to divert also the clearoverflow passing to the mixing device and this clear overflow may bediverted into the spray medium tank.

The mixture normally supplied to the reserve tank as already mentionedis of density slightly greater than that of the primary separating fluidin the separating tank to compensate for variations of density occurringin the separator as would be caused, for instance, by wet screening thefeed to the separator, by a leak in the system, say at a. pump gland, bythe use of sprays to clean the scrapers, particularly the heavy dirtscraper, or by the removal of concentrated accumulations of sandadhering to the heavy dirt or to other separated products. The apparatusfunctions automatically to mix the thickened suspension and clarifiedliquid in such proportions as to return back to the separator asuspension either greater than, equal to, or less than the density ofthe separating suspension according as the latter has been caused tobecome less than, to remain the same as, or to become greater than thatrequired for separation at the desired density. Accordingly the densityof the separating suspension in the separator is automaticallymaintained constant.

The operating density of the densimetric control may be regulated byvarying the effective density of the float by means of the adjustableweights operating on the balance lever as described hereinbefore.

Preferably the float in the densimetric con trol is mounted on a thinrod so that the submerged volume of the float and rod is substantiallyconstant for all positions of the float.

If the level in the reserve or surge tank falls, though this shouldnever occur in normal operation providing the thickening power of thesettling tank is adequate, a visible or audible signal may be given to,the operator and an automatic float may be arranged tocontrol therefilling of the settling tank or of the conditioning chamwith freshsuspension.

The float of the densimetric control need not necessarily be mounted inthe reserve tank as described above but may be arranged in any one of anumber of alternative positions as follows:

Firstly, it may be arranged in the separator itself, preferably in aposition where there is no packing of material to be separated, forexample, in the relatively clear zone between the inlet end and theclean coal discharge as indicated in dotted lines at I05 in Figure 1 orin the further relatively clear zone between the adjustable partitionand the outlet as also indicated in dotted lines at I06 in Figure 1.

According to a further alternative the densimetric control may bearranged in a special compartment or tank in the feed from the reservetank to the separator, i. e. in the pipe TI.

When more than one settling cone or thickener is employed or acombination of settling cone or cones with one or more thickeners, thethickened suspension from one or more cones and/or one or morethickeners may be led to the same conditioning chamber. Moreover,thickened suspension may be pumped to the conditioning chamber insteadof flowing by gravity.

It should be understood that although a thickener in the form of asettling cone has been described, any other form of thickener could beused. Moreover in types of separator such as that described in ourco-pending application No. 338,132, including zones in which suspensionsof difierent densities are employed, the invention may be appliedautomatically to mix the suspensions abstracted from Zones of higher andlower densities to supply to one or other of such zones a suspension ofthe density required to maintain in such zone a constant separatingdensity.

Finally, in a construction of separator as described in our co-pendingapplication No. 338,132, namely, including one or more pockets in thebase of the separator, a densimetric control may be arranged in one oreach of a plurality of such pockets.

What I claim then is: g

1. Gravity separation apparatus of the type specified including aseparating vessel, a thickener for the dilute medium resulting from thespraying of the separated products, a. conditioning vessel, means fordelivering to said conditioning vessel thickened suspension from saidthickener, means for delivering to said separating vessel suspensionconditioned in said conditioning vessel, automatically operating meansfor interrupting said delivery and returning said suspension to thethickener when the density of said suspension falls below that requiredfor delivery to the separating vessel, a counterpoise balance mechanism,means for suspending said conditioning vessel from said mechanism, adischarge conduit leading suspension liquid from said conditioningvessel, superposed chutes arranged to receive liquid from said conduit,the lower chute being associated with means whereby the liquid isconveyed to the separating vessel, and the upper chute leading theliquid back to the thickener, said counterpoise balance mechanism beingadjusted so that if the density of the suspension in the conditioningvessel becomes greater than a predetermined minimum the discharge fromsaid conditioning vessel is directed to the separating vessel, whilst itthe density of the suspension becomes less than said minimum, saidconditioning vessel rises and the discharge therefrom is diverted fromthe reserve tank.

2. Gravity separation apparatus of the type specified including aseparating vessel, a reserve tank, means for circulating separatingsuspension between said separating vessel and said tank, a thickener forthe dilute medium resulting from the spraying of the separated products,a conditioning vessel, means for delivering to said conditioning vesselthickened suspension from said thickener, means for delivering to saidreserve tank conditioned suspension from said conditioning vessel,automatically operating means for interrupting said delivery andreturning said suspension to the thickener when the density of saidsuspension falls below that required for delivery to the separatingvessel, 3, counterpoise balance mechanism, means for suspending saidconditioning vessel from said mechanism, said mechanism being adjustablefor variation oi the coun terbalance of the mechanism in accordance withthe predetermined minimum figure for the density of the suspension inthe conditioning vessel,

an overflow spout near the upper end oi. said conditioning vessel,superposed chutes arranged to receive suspension discharged from saidspout, a lower one of said chutes leading to the reserve tank andreceiving conditioned suspension with a density greater than saidpredetermined minimum, an upper one of said chutes leading back to thethickener and receiving suspension discharged from said conditioningvessel at a density less than said predetermined minimum.

3. Gravity separation apparatus of the type specified including aseparating vessel, a reserve tank, means for circulating separatingsuspension between said separating vessel and said tank, a thickener forthe dilute medium resulting from the spraying of the separated products,a conditioning vessel, means for delivering to said conditioning vesselthickened suspension from said thickener, means for delivering to saidreserve tank conditioned suspension from said conditioning vessel,automatically operating means for interrupting said delivery andreturning said suspension to the thickener when the density of saidsuspension falls below that required for delivery to the separatingvessel, a replaceable nozzle in the flow of thickened suspension fromsaid thickener to said conditioning vessel for adjustment of the saidflow and of the degree of thickening in said thickener, a counterpoisebalance mechanism, means for suspending said conditioning vessel from,said mechanism, said mechanism being adjustable for variation of thecounterbalance of the mechanism in accordance with the predeterminedminimum figure for the density of the suspension in the conditioningvessel, an overflow spout near the upper end of said conditioningvessel, superposed chutes arranged to receive suspension discharged fromsaid spout,

a lower one of said chutes leading to the reserve tank and receivingconditioned suspension with a density greater than said predeterminedminimum, an upper one of said chutes leading back to the thickener andreceiving suspension discharged from said conditioning vessel at adensity less than said predetermined minimum and control means forregulating the admission of clarified liquid to the reserve tank toenable control of the density of the suspension returned to theseparating vessel, said control means including a balance arm, a floatrod on one end of said arm, a densimetric float on said fioat rod, anadjustable counterpoise on the other end of said arm, said float beingimmersedin suspension and mounted for movement to control the operationof electric switch means and electromagnetically operated devicescontrolled by said switch means for regulating liquid flow to saidreserve tank.

4.. Gravity separating apparatus for separating granular materialshaving substantially the specific gravity of coal by means of a mediumof suspension composed of solid particles and a liquid, comprising awashing screen, a thickener,

a separating tank, means for delivering the medium of suspension fromsaid separating tank to said washing screen, means for delivering adiluted liquid medium from the washing screen to the thickener, meansfor discharging the overflow and the underfiow from said thickener,mixer meansmeans for mixing in said mixer means the underfiow with aportion of theoverfiow from said thickener to obtain a mixture which isof greater density than the medium of suspension in the separating tank,means for controlling delivery of the overflow into said mixer inaccordance with the density of the mixture in said mixer, includingmeans for diverting the mixture as it comes from the mixer to saidthickener when it becomes less than the desired density, and means forreturning the mixture to the separating tank after the correct densityhas been secured.

5. Gravity separating apparatus for separating granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension composed of solid particles and a liquid, comprising washingmeans, a thickener, a separating tank, means for delivering the mediumof suspension from said separating tank to said washing means, means fordelivering a diluted liquid medium from said washing means to thethickener, means for discharging the overflow and the underflow fromsaid thickener, mixer means, means for mixing in said mixer means theunderilow with a portion of the overflow from said thickener to obtain amixture which is of greater density than the medium of suspension,automatic means for controlling delivery of the overflow into said mixerin accordance with the density of the mixture in said mixer, includingautomatic means for diverting the mixture as it comes from the mixer tosaid thickener when it becomes less than the desired density, and meansfor returning the mixture to the separating tank after the correctdensity has been secured.

6. Gravity separating apparatus for separating granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension composed of solid particles and a liquid comprising aseparating tank, a thickener, means for delivering the medium ofsuspension from said separating tank to the thickener, means fordischarging the overflow and the underiiow from said thickener, mixermeans, means for mixing in said mixer means the underflow with a portionof the overflow from said thickener to obtain a mixture which is ofgreater density than the medium of suspension in the separating tank,automatic means for controlling delivery of the overflow into said mixerin accordance with the density of the mixture in said mixer, includingmeans for diverting the mixture as it comes from the mixer to saidthickener when it becomes less than the desired density, and means forreturning the mixture to the separating tank after the correct densityhas been secured.

7. Gravity separating apparatus for separatin'g granular materialshaving substantially the specific gravity of coal by means of a mediumof suspension composed of solid particles and a liquid, comprising aseparating tank, a thickener, and spraying means, for delivering themedium of suspension from said separating tank to said spraying means,means for delivering a diluted liquid medium from the spraying means tothe thickener, means for discharging the overflow from the underflow tosaid thickener, mixer means, means for mixing in said mixer means theunderflow with a portion of the overflow from said thickener to obtain amixture which is of greater density than the medium of suspension in theseparating tank, automatic means for controlling the delivery of theoverflow into said mixer in accordance with the density of the mixturein said mixer, including automatic means for diverting the mixture as itcomes from the mixer to said thickener when it becomes less than thedesired density, and means for returning the mixture to the separatingtank after the correct density has been secured.

8. Gravity separating apparatus for separating granular materials havingsubstantially the specific gravity 01 coal by means of a medium ofsuspension composed of solid particles and a liquid, comprising awashing screen, a thickener, a separating tank and a reserve tank, meansfor delivering the medium of suspension from said separating tank tosaid washing screen, means for delivering a diluted liquid medium fromthe washing screen to the thickener, means for discharging the overflowand the underflow from said thickener, mixer means, means for mixing insaid mixer means the underflow with a portion of the overflow from saidthickener to obtain a mixture which is of greater density than themedium of suspension in the separating tank, means for controllingdelivery of the overflow into said mixer in accordance with the densityof the mixture in said mixer, including means for diverting the mixtureas it comes from the mixer to said thickener when it becomes less thanthe desired density, means for returning the mixture to the separatingtank after the correct density has been secured, and means fordelivering to said reserve tank conditioned suspension from said mixer.

9. A method of gravity separation for granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension of solid and liquid, including the steps of leading away froma separation vessel a medium of suspension, diluting said medium ofsuspension, thickening the diluted medium within a thickener,discharging the overflow and underflow from the thickener, mixing theunderflow with a portion of the overflow to obtain a mixture which is ofgreater density than the medium in the separating vessel, controllingthe delivery of the overflow into a mixing vessel in accordance with thedensity of the mixture, diverting the mixture to the thickener when itbecomes of less density than desired and returning the mixture to theseparating vessel after proper density has been secured.

10. A method of gravity separation for granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension of solid and liquid, including the steps of leading away froma separation vessel a medium of suspension, screening and diluting saidmedium of suspension, thickening the diluted medium within a thickener,discharging the overflow and underflow from the thickener, mixing theunderflow with a portion of the overflow to obtain a mixture which is ofgreater density than the medium in the separating vessel, controllingthe delivery of the overflow into a mixing vessel in accordance with thedensity of the mixture, di-

- verting the mixture to the thickener when it becomes of less densitythan desired and returning the mixture to the separating vessel afterproper density has been secured.

11. A method of gravity separation for granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension of solid and liquid, including the steps of leading away froma separation vessel a medium of suspension, screening said medium ofsuspension, thickening the screened medium within a thickener,discharging the overflow and underflow from the thckener, mixing theunderflow with a portion of the overflow to obtain a mixture which is ofgreater density than the medium in the separating vessel, controllingthe delivery of the overflow into a mixing vessel in accordance with thedensity of the mixture, diverting the mixture to the thickener when itbecomes of less density than desired and returning the mixture to theseparating vessel after proper density has been secured.

12. A method of gravity separation for granular materials havingsubstantially the specific gravity of coal by means of a medium ofsuspension of solid and liquid, including the steps of leading away froma separation vessel a medium of suspension, diluting said medium ofsuspension, thickening the diluted medium within a thickener,discharging the overflow and underflow from the thickener, mixing theunderflow with a portion of the overflow to obtain a mixture which is ofgreater density than the medium in the separating vessel, controllingthe delivery of the overflow into a mixing vessel in accordance with thedensity of the mixture and returning the mixture to the separatingvessel after proper density has been secured, but interrupting thereturn of the mixture to the separating vessel and diverting saidmixture to the thickener when the density of the mixture falls below thedesired density, again discharging the overflow and underflow from thethickener, mixing the underflow with a portion of the overflow to obtaina mixture which is of greater [density than the medium in the separatingvessel and returning the mixture to the separating vessel after properdensity has been secured.

ARTHUR ALGERNON HIRST.

